Hey guys, need some help controling a solenoid with an optical switch.
I want the current to the solenoid to be OFF when the optical switch is blocked, ON when clear.
I've build the attached circuit and I can get a voltage drop when I block the sensor but I can't get the transistors to turn on when the sensor is open.
I'm using HY860F optical switch and I can't find a datasheet.
hi,
The gain of the 2N3055 is very low in saturation, say 5 to 10, you have a 1K base resistor to 12V, thats only giving a 10mA base current to the 2N3055.
You can't possibly get 5A through the solenoid from a 12V supply with a 100Ω resistor in the 3055's emitter path. Have you considered using a power MOSFET instead of a 3055?
It should work better if you change the 2N3055 to a power NMOSFET. Also make the collector resistor of Q1 about 1kΩ and remove the emitter resistor (or make it perhaps 10k-100kΩ).
Thanks guys, I will redesign with a NMOSFET and let you review. I've been out of electronics for quite a while (30 years!) and need all the help I can get.
If you want the plunger to move at a fairly constant speed that will be difficult because of plunger friction and inertia. I think it would entail having a high current at switch-on, to overcome stiction, followed by a rapid ramped reduction in current to reduce acceleration to zero. IMO the circuit to do that will need more than just an added cap.